1. Field of the Invention
The invention relates to cylindrical filters and their manufacture.
A cylindrical filter is customarily formed from a sheet of filter media joined along two opposed edges to form the cylinder. The media may be in the form of a plain sheet or the sheet may be corrugated, in which case the joined edges are the final corrugations.
2. Brief Review of the Prior Art
The joint is customarily made by contacting the areas of the sheet adjacent the two edges and then forming a seal between these areas. In general, the overlap will be with the edges in register, particularly where the sheet is pleated. Such a sealed joint is acceptable where the sheet is formed from a single layer of filter media. It is, however, less satisfactory where the sheet is formed from two superimposed layers of media connected together. In this case, the possibility of a flow path through a single seal is increased.
In EP-A1-0001407 there is disclosed the joining of the edges of a sheet formed of two superimposed layers of media connected together and utilizing a channel strip for connecting the layers of media together. In U.S. Pat. No. 3,865,919 a number of corrugations of a pleated sheet of filter material are bonded together and then provided with a tape or ribbon of adhesive in a space formed between the corrugations. The adhesive is melted to form a leak-proof seal.